Elevated atmospheric carbon dioxide effects on sorghum and soybean nutrient status 1

Increasing atmospheric carbon dioxide (CO₂) concentration could have significant implications on technologies for managing plant nutrition to sustain crop productivity in the future. Soybean (Glycine max L.] Merr.) (C3 species) and grain sorghum (Sorghum bicolor L.] Moench) (C4 species) were grown in a replicated split‐plot design using open‐top field chambers under ambient (357 μmol/mol) and elevated (705 μmol/mol) atmospheric CO₂. At anthesis, leaf disks were taken from upper mature leaves of soybean and from the third leaf below the head of sorghum for analysis of plant nutrients. Leaf greenness was measured with a Minolta SPAD‐502 chlorophyll meter. Concentrations of chlorophylls a and b and specific leaf weight were also measured. Above‐ground dry matter and seed yield were determined at maturiry. Seed yield of sorghum increased 17.5% and soybean seed yield increased 34.7% with elevated CO₂. There were no differences in extractable chlorophyll concentration or chlorophyll meter readings due to CO₂ treatment, but meter readings were reduced 6% when sorghum was grown in chambers as compared in the open. Leaf nitrogen (N) concentration of soybean decreased from 54.5 to 39.1 g/kg at the higher CO₂ concentration. Neither the chambers nor CO₂ had an effect on concentrations of other plant nutrients in either species. Further work under field conditions is needed to determine if current critical values for tissue N in crops, especially C3 crops, should be adjusted for future increases in atmospheric CO₂ concentration.